Increase the size for the demangled symbol buffer to 8192 bytes

Previously the 1024 bytes was potentially too small for some complex
rust symbols leading to failures in demangling.

Bumping this to 8x should reduce the chances for this, but still
gives off a strong "640K Ought to be Enough for Anyone" vibe :)

Fixes: KDAB/hotspot#611
Change-Id: Ib08f7fce59766e4ed7fef094ea0a61d040e3fceb

app/perfdwarfdiecache.cpp

@@ -236,7 +236,7 @@ QByteArray demangle(const QByteArray &mangledName)
     if (mangledName.length() < 3) {
         return mangledName;
     } else {
-        static size_t demangleBufferLength = 1024;
+        static size_t demangleBufferLength = 8192;
         static char *demangleBuffer = reinterpret_cast<char *>(eu_compat_malloc(demangleBufferLength));
         static Demangler demangler;